1. Field of the Invention
The present invention relates to a vehicle driving force control device for controlling a driving force to appropriately maintain a grip force of a vehicle wheel in various running conditions such as when a vehicle is in a starting mode, a straight running mode, or a turning mode.
2. Description of the Related Art
Various kinds of traction control devices for limiting the driving force to restrain a slipping of the vehicle wheel have been proposed and put to practical use.
For example, Japanese Unexamined Patent Application Publication No. 5-214974 discloses a technology where a slip rate of a drive wheel is calculated on the basis of the speed of the drive wheel and the speed of the vehicle body, and the engine output torque is reduced when the slip rate has exceeded a predetermined threshold value so as to perform feedback control on the throttle valve to restrain an excessive slipping of the drive wheel.
When a vehicle corners, a lateral force acting on a tire increases, whereas a permissible longitudinal driving force and the slip rate for maintaining a stable vehicle behavior decrease. Therefore, in a traction control device such as the one disclosed in Japanese Unexamined Patent Application Publication No. 5-214974, although it is necessary to detect a minute amount of slipping of the tire during cornering to stabilize the vehicle behavior, such detection is difficult since there is a limitation in the calculation accuracy for estimating the ground speed of the vehicle body. This makes it difficult to reduce the driving force to maintain the stability of the vehicle by determining a torque-down amount with high precision.